1. Field of the Invention
This invention relates generally to the conversion of methanol so as to produce gasoline boiling-range hydrocarbons and, more particularly, to a process for maximizing gasoline production and minimizing catalyst deactivation by splitting the conversion reactor into a series of smaller units.
2. Description of the Prior Art
The conversion of methanol-to-gasoline boiling-range hydrocarbons is well known in the prior art. A conventional methanol-to-gasoline system, as disclosed in U.S. Pat. No. 3,928,483 (Chang et al) dated Dec. 23, 1975, consists of two or more reactors in a series. Generally, in the condensation reactor stage methanol is reacted over a condensation catalyst to produce a reaction product containing aliphatic dehydration products and water. In the conversion stage a portion of the reaction products of the first stage are contacted with a crystalline aluminosilicate zeolite catalyst to convert the reaction products to gasoline range hydrocarbons.
U.S. Pat. No. 3,931,349 (Kuo) dated Jan. 6, 1976, discloses a two stage process for converting methanol-to-gasoline where the exothermic temperature rise in the first stage is catalytically restricted and a heat dissipating diluent is employed in the second stage.
U.S. Pat. No. 3,998,899 (Daviduk et al) dated Dec. 21, 1976, shows a process for passing methanol through a plurality of catalyst contact zones which are temperature restrained in response to catalyst activity and selectivity.
U.S. Pat. No. 4,083,889 (Caesar et al) dated Apr. 11, 1978, shows a method for converting methanol-to-ethylene in the presence of steam and a ZSM-5 catalyst at a temperature of about 600.degree. to about 750.degree. F.
U.S. Pat. No. 4,035,430 (Dwyer et al) dated July 12, 1977, discloses a method of converting methanol-to-gasoline boiling products in a plurality of sequentially arranged catalyst beds. One catalyst bed contains a calcined alumina which dehydrates the methanol charge to produce a dimethyl ether product, unconverted methanol, and water. Dimethyl ether is passed through a second series of catalyst contact zones comprising a plurality of catalyst beds in a single reactor.
U.S. Pat. No. 4,049,734 (Garwood et al) dated Sept. 20, 1977, discloses a two step process for methanol conversion where synthesis gas is converted in a first stage to a product comprising methanol. Methanol is then converted to an aromatic gasoline product over a zeolite catalyst at a temperature of about 500.degree.-1200.degree. F.
U.S. Pat. No. 4,058,576 (Chang et al) dated Nov. 15, 1977, discloses a multiple stage catalyst process for converting methanol to olefins and/or gasoline boiling components. The reaction stages proceed through methanol conversion to dimethyl ether, ether conversion to olefins, and conversion of olefins to gasoline boiling components.
U.S. Pat. No. 4,138,442 (Chang et al) dated Feb. 6, 1979, discloses a process where methanol is reacted with a zeolite catalyst to produce a product which is resolved into a high octane gasoline fraction and other products.
U.S. Pat. No. 4,263,141 (Moller) dated Apr. 21, 1981, discloses a methanol-to-gasoline step process wherein the methanol is catalytically converted into gasoline hydrocarbons. The reaction takes place over known zeolite catalysts and the gasoline synthesis stage may consist of one or more tubular reactors.
In conventional conversion reactor systems most of the methanol conversion occurs in the upstream one-third to one-half of the catalyst bed. Under standard reactor conditions of high temperature and high pressure, water in the form of steam which results from the conversion process and from water occurring naturally in the feed flows throughout the catalyst bed deactivating the catalyst. Unlike coking-type deactivation where the catalyst can be regenerated by burning off the coke, steam deactivation is permanent and the catalyst activity is not recoverable. Therefore, it is an object of this invention to produce an improved methanol-to-gasoline conversion process wherein the downstream portion of the catalyst bed is not prematurely and permanently deactivated by steam. The advantages of such an invention are particularly apparent from an economic point of view. By preventing the catalyst from becoming prematurely deactivated, the reactor will operate far more efficiently and economically; and reactor shut down rate will be drastically reduced as well as the man hours required in replacing the permanently deactivated catalyst.